Process for drying higher fatty acid sarcosines



Oct. 13, 1964 J. A. MONICK ETAL PROCESS FOR DRYING HIGHER FATTY ACIDSARCOSINES Original Filed July 7, 1958 2 Sheets-Sheet 1 JNVENTORSJOH/VAZEXflNDfR MON/CK W/lU/lMl/UBLRTLEHMACHER I g ATTORNEY Oct. 13,1964J. A. MONICK ETAL 3,152,947

PROCESS FOR DRYING HIGHER FATTY ACID SARCOSINES Original Filed July 7,1958 2 Sheets-Sheet 2 zlvvswozzs JOH/VALfXANDER ON/CKVWZU/IMHUBERTLEHMHCHER BY MM ATTORNEY United. States Patent The presentinvention relates to a process for heat drying aqueous solutions ofhigher fatty acid sarcosines and salts thereof.

Higher fatty acid sarcosines are useful as constituents I of dentalpreparations such as tooth pastes and powders,

in detergent bars, and like compositions.

For a number of such uses, e.g. incorporation in tooth powders and drydetergent compositions, it is desirable that the higher fatty acidsarcosine be available in dry solid form, preferably a particulate solidform. The fatty acid sarcosines and their salts are more stable towardchemical and biological decomposition when in dry solid form than whenin the form of an aqueous solution.. Also, when the product must betransported shipping costs are lower. Inasmuch as the usualmanufacturing process produces the higher fatty acid sarcosines inaqueous solution, a drying step is necessitated. However, due to thepeculiar properties of the-higher fatty acid sarcosines and concentratedsolutions thereof, the drying of such solutions presents a troublesomeproblem.

Higher fatty acid sarcosines are difficult to dry satisfactorily byconventional methods because of their tendency to decompose on exposureto elevated temperatures for an extended period of time. sarcosines arealso characterized by a tendency to gel when in high concentrations inaqueous solutions. Such gels are characterized by very poor heat andmass transfer rates, and are very difficult to dry without experiencingthermal decomposition of the sarcosine.

The higher fatty acid,

ice

.The normally solid sarcosines contemplated as within the presentinvention are amides formed from sarcosine and a higher fatty acid ormixtures thereof. These fatty acids are straight chain highermono-carboxylic acids containing from to 18 carbon atoms and may besaturated or unsaturated as long as the sarcosine derivative or saltthereof is normally solid. Examples of such fatty acids are lauric acid,myristic acid, palmitic acid, oleic acid,

It has previously been proposed to overcome these 7 of the zone as isamixture of spent drying gas and cooling air.

A process for heat drying aqueous higher fatty acid sarcosines and theirsalts has now been discovered which is characterized by advantages ofreduced thermal decomposition during processing, substantially"quantitative recovery of fatty acid sarcos-ine solids (c.g. greaterthan 99%) and the production of dust-free dry products.

coconut oil fatty acids, and hydrogenated. tallow fatty acids, it beingespecially preferred to carry out the present process employing thosefatty acid sarcosines which either because of their relatively lowstability, low melting point or tendency to gel, or combination of suchcharacteristics, cannot be dried in conventional ways into discrete,non-dusty particles. Examples of sarcosines which readily form gels whenin high concentration in aqueous solution are those higher fatty acidsarcosines prepared from straight chain saturated fatty acids containing12 to 16 carbon atoms, and especially the sodium salts thereof.

The sarcosines of the present invention may be in the acid form or maybe employed as a salt (sarcosinate) and the term higher fatty acidsarcosine as used herein and in the appended claims is intended toencompass Within its scope both the acid' and its salts. It is preferredto employ salts selected from those formed by alkali metals ornitrogen-containing radicals. More particularly they may be sodium,potassium, ammonium, amine, niono-, di, or tri-ethanolamine salts. It isparticularly preferred to carry out the present process employing thesodium salts of sarcosinates whose fatty'acyl groups are saturated andcontain from 12 to 16 carbon atoms.

The presenthigher fatty acid sarcosines may be made by condensing afatty acid chloride'or a mixture of fatty acid chlorides with sarcosinein thepresence of a hydrogen halide acceptor, e.g. caustic soda, sodaash, magnesium hydroxide, trimethyl amine. The resulting amide isseparated, acid washed and subsequently, if desired, neutralized with a.base containing a desired cation. Ordinarily the sarcosine orsarcosinate is obtained in solution, and to promote economical drying ofsuch a formed at room temperature and above, such a gelationconcentration is the upper feasible solution concentration limit of theaqueous solutions dried in carrying out the present process. Theaddition of solvents such as ethanol and isopropanolis within the scopeof the present invention as these solvents are removed along withNegligible increase in free fatty acid content is experienced in thecourse .of drying higher fatty acid sarcosines in accordance with thepresent procedure, thus facilitatingpreparation of higher fatty acidsarcosiues containing less than- 15% free fatty acid, (or fatty acid 1soap) which is preferred for use in dentifrices.

lnaccordance with the present invention a continuous V processfor heatdrying a higher fatty acid sarcosine comprises forming a thinlayer of afluid aqueous solution of a higher'fatty acid sarcosine, heating saidlayer to a temperature sufiicient to boil off the water therein and meltsaid higher fatty acid sarcosine for a time sufiicient higher fatty acidsarcosine substantially pure and containing from 10 to 48% total.solids.

The word solution is used herein to describe fluid aqueous preparationsincluding true solutions, suspensions, collodial suspensions,dispersions, and slurries, but

is exclusive of gels. These aqueous solutions may contain other'liquidingredientssuch as low molecular weight alcohols, e.g. ethanol and ,isopropanol whichserve to diminish solution viscostiy and toy increase theextent of fatty acid sarcosinate solubilty without gel formation,

bacteria or microorganisms.

as fillers, additives or impurities which do not significantly detractfrom the utility of the product or seriously interfere with the presentprocess, however, when intended for I used in dental preparations forits acid inhibiting effect the sarcosine should be as free as possibleof fatty acids and fatty acid soaps because of the deactivatingproperties thereof.

In carrying out the instant drying procedure, the fluid aqueous higherfatty acid sarcosine, preheated if desired but normally at a temperaturebelow about 100 C., is disposed as a thin moving layer of liquid fromwhich solvent is vaporized as the layer progresses through a heatingzone. The layer employed is preferably disposed on a heated metallicsurface and is less than A inch thick, preferably being a thin filmhaving a thickness of less than inch, typically between and of an inch.In the previously mentioned heated zone the layer of higher fatty acidsarcosine is heated to a temperature which is above the boiling point ofthe solvent from the aqueous layer and above the melting point of thehigher fatty acid sarcosine solid, typically to a temperature on theorder of 145195 C., in the case of the salts, and 105145 C. in the caseof the lower melting free acids.

As the layer progresses through the heated zone it is maintained at atemperature above its boiling point for a period of time sufficient forsubstantially all of the solvent therein to evaporate or boil off, andto form substantially dry molten fatty acid sarcosine, but insuflicientto cause any significant pyrolytic decomposition of the higher fattyacid sarcosine. Typically, such a period of time of exposure to elevatedtemperature is on the order of less than 2 minutes, and preferably lessthan 30 seconds, typically being on the order to to 30 seconds. Themolten higher fatty acid sarcosine is then removed from the heated zoneand immediately is cooled to a stable solid condition to form a rigidsolid product containing less than about 6%, and preferably less thanabout 2% moisture as at moisture levels of about 6.5% and above,non-rigid tacky gels tend to form.

The thin layer of higher fatty acid sarcosine which is processed inaccordance with the present invention is agitated throughout the boilingperiod. While suitable turbulence may be obtained by means of turbulentfluid flow, it is much preferred to carry out the instant processemploying mechanical agitation of a thin film of liquid being heated ona metallic surface.

The dry molten fatty acid sarcosine may be cooled in any suitable mannerto form flakes, pellets, ribbons, powder, granules, spheres, strips,bulk form, or the like. It is preferred to form dense, non-dusty readilysoluble solid pellets of maximum diameter less than about inch byforming the molten fatty acid sarcosine into discrete liquid dropletswhich are solidified by spray cooling, immersion in a cool, non-solventliquid, or deposition on a chilled surface, e.g. a cooling roll. Suchdense particulate solids have a high bulk density and are economical toship, and are readily wetted by water, dissolving easily withoutfloating or foaming.

In order to indicate more specifically the advantages and features ofthe novel process of the present invention, the following examples areset forth, which taken in conjunction with the accompanying drawings,illustrate preferred form of apparatus for carrying out the presentinvention. In these examples all parts and percentages are by weightunless otherwise specified.

Example 1 FIG. 2 is a section taken on line 22 of FIG. 1; and

FIG. 3 is a section taken on line 33 of FIG. 1.

The apparatus of FIGS. 1-3 comprises a wiped film evaporator 18, acooler 20, and a product collection bin 22. The wiped film evaporatorcomprises essentially a closed vertically elongated tube 38 containing aconcentrically mounted rapidly rotating vaned agitator 40 which forcesthe liquid content of the evaporator against the inner wall of saidvertical elongated tube 38 thus spreading the liquid in a thin film andmaintaining the liquid in rapid movement so as to insure intimatemixing, heat transfer and prevent overheating. A feed supply nozzle 36is located in the upper portion of the tube 38. The portion of thevertical tube 38 below the feed point 36 of the evaporator 18 isprovided with a jacket 39 through which a heating medium is passed, theheating medium entering and leaving said jacket by means of taps 44 and46 at the base and top thereof respectively. The liquid content of theevaporator flows down the inside surface of the tube $8, through aspider 48 which carries a foot bearing 49 supporting the vaned agitator4t}, and collects in a closed cylindrical distributor 50 which isprovided with perforations 51 near the outer edge of the base thereof.The distributor is steam traced (not shown) in order to, prevent coolingand solidification of the material therein.

Liquids passing through the perforations fall as droplets on a rotatingdrum 52 which is chilled by cooling water supplied to the interiorthereof through hollow trunnions 54 and 56. Material is removed from thesurface of the cooling roll by a doctor blade 58, and falls into theproduct collection bin 22.

The portion of the vertical elongated tube 38 above the feed point 36forms a separation chamber 60 for recovery of liquid entrained in thevapors being removed. A conduit 62, which communicates with theseparation cham ber 69, is connected to a source of slight vacuum (onthe order of 4 millimeters of water) so as to facilitate removal ofsolvent vapors from the reactor 18. The vaned agitator 40 is rotated bya belt 64 driven byan electric motor 66.

In operation a 36% fluid aqueous solution of (99% sodium N-lauroylsarcosinate and 1% lauric acid soap) solids is fed at room temperatureof 25 C. to the evaporator through the feed conduit 36-at a rate ofpounds of solution per hour for a 4-hour period. Rapid rotation of theagitator spreads and turbulently agitates the solution as a thin film onthe interior of wall 38 of the evaporator, the clearance between theperiphery of the vanes 40 and wall 38 and the thickness of the filmbeing approximately A2 inch. Saturated steam at p.s.i.g. (C.) issupplied to the jacket through tap 46, and condensate is removed at tap44.

Vapors at a temperature of 102 C. v are removed through conduit 62 byapplication thereto of a vacuum of 4 millimeters of water. Thevaporizing surface in the evaporator is 9 square feet, and the agitatorruns at 900 r.p.rn., corresponding to a peripheral velocity of 2,820

feet per minute at the outer edges of the vanes. Molten,

substantially dry sodium N-lauroyl sarcosinate issues from the base ofthe evaporator and falls into the distributor head 50 from which itissues as droplets through the holes 51 and falls onto the cooling roll52, the time of passage from the feed conduit to the cooling roll beingapproximately 22 seconds. The holes inthe distributor. are made by a No.30 drill, and the pellets which form on the cooling roll are flatteneddroplets approximately A inch thick and of an inch in diameter. Thepellets are removed from the cooling roll at approximately 25 C. by the.doctor blade'58 and fall into the collection bin 22.

Analysis of the product obtained in the collection bin discloses thatthere has been no increase in the soap content during processing. Theproduct contains 97.6% sodium N-lauroyl sarcosinate, 1.0%1auric acidsoap, and

soap.

Example II The procedure of Example I is repeated employing a fluid feedsolution containing 39.6% sodium N-lauroyl sarcosinate, 0.4% sodiumlaurate, 40% Water, and 20% ethanol at room temperature. The feed rateis 30 pounds per hour per square foot of heated surface in theevaporator, and the evaporator is heated with saturated steam at 'about145 C. No increase in soap content is experienced, the product beingsolid, free-flowing, non-tacky, rigid, alcohol-free particles whichcontain 93.25% sodium N-lauroyl sarcosinate, 5.75% moisture, and 1.0%

Example 111 The procedure of Example II is repeated employing, as afeedstock, a fluid mixture containing 85% molten N- lauroyl sarcosine(melting point about 45 C.) and 15% water. The feed rate is 2.0 poundsper hour per square foot of heated surface, and the temperature of theteed is about 75 C. The saturated steam used is at about 127 C. Theproduct obtained contains 98.2% N- lauroyl sarcosine, 1.5 free fattyacid, and 0.3% moisture.

Example IV Example V FIG. 4 shows diagrammatically the variouscomponents of an alternate apparatus for carrying out the process of thepresent invention. It comprises a commercially available thin filmheater '70 constructed in a manner similar-to a conventional plate andframe filter 'press that it consists of a plurality of thin corrugatedrectangular sheets 72 clamped between two end plates 74, '76 (by meansnot shown), a centrifugal liquid-vapor I separator 77, a liquiddistributor 7 8, a product cooler 79,

and a collection bin $0. v

FIG. 5 illustrates a typical construction of one of the sheets '72." Thesheets are spaced and sealedby gaskets 81 around their outer edges andare provided, in a manner similar to the plates of a conventional plateand frame filter press, with openingsiZ, S3, 84 and 85 in each cornerfor flow of fluid. These openings may be communicated with or sealed offfrom the space between any pair [of adjacent plates by virtue of theshape of the gaskets blemployed. Thus in the embodiment illustrated inFIG. 5, openings tvit and d5 communicate with the illustratedsurfaceofthe plate 72,-and openings 82 and 84 head dispense droplets onto thecooler 79.

space between surfaces of adjacent plates. The plate to plate spacingthroughwhich the fluid flows averages from $4 to of an inch, thusproviding, in the space between each pair of plates, for the formationof a turbulently flowing stream consisting, in essence, of two liquidlayers each from A to of an inch thick.

The heater of FIG. 4 is provided with a conduit 88 through which heatingmedium is supplied to the plates and a conduit 89 for exhausting theused heating medium. A conduit 90 supplies feed to be heated to thespaces between the plates, and a conduit 92 is provided for removal ofthe heated product.

The product conduit 92 is tangentially connected into the periphery of acentrifugal separator 77 comprising a closed cylindrical vessel 94;provided with an overhead line 98 for removal of vapors and a drainconduit 100 for removal of liquids. A center post 102 is provided tomaintm'n regular circulation of materials in the separator and toprevent turbulence.

The drain conduit 100 supplies the distribution head 78. Perforations101 in the bottom of the distribution In use, the separator 77, thedrain conduit 100, and the distribution head 78 are steam traced (notshown) to insure that the materials therein are maintained in moltencondition.

The cooler 79 comprises a cooling roll 104 which is chilled by means ofcold water supplied-thereto through hollow trunnions 106 and 108. Cooledmaterial is removed trom the surface of the cooling roll by a doctorblade 119 and falls into the collection bin 80.

In operation a 38% aqueous solution of 98.5% sodium 'N-lauroylsarcosinate and 1.5% sodium laurate is fed to as a heating medium and ispassed through the space between alternate pairs of plates. The solutionboils in the heater and forms a mixture of steam and molten so diumN-lauroyl sarcosinate which issues from the heater through conduit 92and passes into the centrifugal separator 77. Water vapors are removedfrom the separator through the overhead line 98 by the applicationthereto of a vacuum of 4 millimeters of water, and liquid sodiumN-lauroyl sarcosinate drains from the base of the separator through thedrain conduit 190 into the distributor 78. Droplets of sodium N-lauroylsarcosinateissue from the distributor, fall onto the cooling roll104where they are immediately cooled'below their solidification pointand form. small solid pellets, and are removed from the roll by thedoctor blade and collected in the pan 80. The total time of passage fromthe feed conduit 90 to the cooler 79 is on the order'ot less than 45seconds.

The pellets produced contain 95% sodium N-lauroyl sarcosinate, 2.5%lauric acid soap, and 2.5% moisture.

The effectiveness of heating the material being dried to a temperatureabove its melting point, as in the foregoing examples, is illustrated bysimulating the procedure of .EXarnple I using as a heating medium,saturated steam ployed. I The solution concentrates only" to about 40%solids, and themes it approaches the gel condition, be-

comes so viscous that it cannot be removed from the The advantages ofthe present base of the evaporator. I process which readily producesafree-flowing, substantially-dry molten product are apparent. I 3' i Thisapplicaiton is a continuation of our pending application SN. 746,763,filedjluly 7, 1958, now abandoned.

What is claimed is:

l. A continuous process for heat drying of fluid aque ous solution of anormally rigid solid higher fatty acid sarcosinate which comprisesmoving such solution turbulently over a heated metallic surface indirect contact therewith, heating said solution thereby to a temperatureabove both the boiling point of the solution and the melting point ofthe sarcosinate, vaporizing substantially all of the aqueous solventfrom said solution and melting the substantially dry sarcosinate thusformed before contact with any substantial amount of gas other than saidvapor, forming the molten dried sarcosinate into discreteliquiddroplets, and cooling said droplets to rigid solid pellets of drysarcosinate.

2. A containuous process for heat drying of fluid aqueous' solution of anormally solid rigid higher fatty acid sarcosinate as set forth in claim1 in which the solution is moved turbulently as a wiped layer.

3. A continuous process for heat drying of fluid aqueous solution of anormally rigid solid higher fatty acid sarcosinate as set forth in claim1 in which the solution is caused to move turbulently by frequentchanges in cross sectional area as it flows between adjacent heatingareas of said metallic surface.

4. A continuous process for converting an aqueous solution of sodiumN-lauroyl sarcosinate at a solids concentration within the range ofabout to 40% into solid pellets having a moisture content not exceedingabout 6% as set forth in claim 3 in which said stream is a thin wipedcylindrical layer and the vapor is separated countercurrently tosaidmoving stream of solution as it is formed.

5. A continuous process for converting an aqueous solution of sodiumN-lauroyl sarcosinate at a solids concentration within the range ofabout 10% to 40% into solid pellets having a moisture content notexceeding about 6% as set forth in claim 3 in which said streamfrequently changes in direction and cross-section and the vapor anddried molten sarcosinate move concurrently until they are separated andthe separation takes place by centrifugal action.

6. A continuous process for converting an aqueous solution of sodiumN-lauroyl sarcosinate at a solids concentration within the range ofabout 10% to 40% into solid pellets having a moisture content notexceeding about 6% which comprises moving a stream of said solutioncontinuously through a passageway, agitating and.

rapidly heating said solution as it moves through said passageway to atemperature within the range of about 145 to 195 C. for a period on theorder of less than 2 minutes whereby aqueous solvent is converted intovapor until not more than 6% moisture is present in the sarcosinate andthe thus dried sarcosinate is in molten conditi'on, separating saiddried molten sarcosinate from said vapor before contact with anysubstantial amount of gas other than said vapor, forming said separateddried molten sarcosinate into discrete droplets, and cooling said droplets to solid pellets of sodium N-lauroyl sarcosinate con; taining notover 6% moisture.

7. A'continuous process for heat drying, with minimum thermaldecomposition, an aqueous higher fatty acid sarcosinate salt which isnormally a rigid solid'comprising forming a flowable non-gelled aqueoussolution of a normally solid higher fatty acid sarcosinate salt havingatendency to gel when in aqueous solution at high concentration,disposing said flowable sarcosinate solution as a'wiped liquid film,turbulently agitating and I rapidly heating said film of sarcosinatesolution to a'temperature. aboveboth'the boiling point of the solutionforming said film and the melting point of said higher fatty acidsarcosinate salt, vaporizing substantially all of the water in said filmto produce said higher fatty acid sarcosinate in molten, substantiallydry form, forming droplets of said sarcosinate and immediately coolingsaid droplets to a temperature below its melting point to form higherfatty acid sarcosinate salt in the form of rigid, substantially dry,non-tacky pellets substantially free of any thermal degradation product.

8. A continuous process for heat drying an aqueous higher fatty acidsarcosinate as set forth in claim 7 wherein said sarcosinate is sodiumN-lauroyl sarcosinate.

9. A continuous process for heat drying, with minimum decomposition, anaqueous higher fatty acid sarcosinate which is normally a rigid solidcomprising forming, at a temperature below C., an aqueous solutioncontaining from about 10 to 40% by weight of a higher fatty acidsarcosinate, said fatty acid being a straight chain monocarboxylic acidcontaining from 12 to- 16 carbon atoms, disposing said solution as awiped liquid film less than inch thick on a heated metallic surface,turbulently agitating and rapidly heating said film to a temperatureabove the melting point of said sarcosinate for a period of from 10 to30 seconds sufiicient to boil oif substantially all of the water thereinand produce said higher fattyacid sarcosinate in molten, substantiallydry fornn forrning droplets of said sarcosinate and immediately coolingsaid droplets to a temperature below about 40 C. to produce hi her fattyacid sarcosinate in the form of rigid, substantially dry, non-tackypellets substantially free of any pyrolytic degradation product.

10. A continuous process for heat drying an aqueous solution of anormally rigid solid higher fatty acid sarcosinate which comprisesmoving turbulently a wiped layer of a fluid aqueous solution thereofover a heated surface, heating said layer to a temperature above boththe boiling point of said solution and the melting point of said fattyacid sarcosinate, vaporizing substantially all of the water in saidlayer and melting the substantially dry fatty acid sarcosinate thusformed, forming said molten fatty acid sarcosinate into discrete liquiddroplets, and cooling said droplets to rigid solid pellets of dry,higher fatty acid sarcosinate.

11. A continuous process for heat drying an aqueous solution of a higherfatty acid sarcosinate as set forth in claim 10 wherein said higherfatty acid sarcosinate is sodium N-lauroyl sarcosinate.

12. A continuous process for heat drying an aqueous solution of a higherfatty acid sarcosinate as set forth in claim 10 wherein said higherfatty acid sarcosinate is sodium N-palmitoyl sarcosinate.

' References Cited in the file of this patent UNITED STATES PATENTS788,446 Wilson Apr. 25, 1905 868,447 Just Oct. 15, 1907 1,165,677 KingDec. 28, 1915 1,837,702 Canfield Dec. 22, 1931 2,341,258 Appel Feb. 8,1944 2,643,180 Miller June 23, 1953 2,751,338 Schwemberger June 19, 19562,812,019 Rasmussen Nov. 5, 1957 2,817,155 Gilliam et al. Dec. 24, 19572,830,064 Monick Apr. 8, 1958 2,844,607 Gushin et al. July 22, 19582,863,888 Schurman Dec. 9, 1958 2,873,799 Barley et al. Feb. 17, 19592,890,155 Bueche June 9, 1959 FOREIGN PATENTS 740,825 Great Britain Nov.23, 1955

1. A CONTINUOUS PROCESS FRO HEAT DRYING OF FLUID AQUEOUS SOLUTION OF ANORMALLY RIGID SOLID HIGHER FATTY ACID SARCOSINATE WHICH COMPRISESMOVING SUCH SOLUTION TURBULENTLY OVER A HEATED METALLIC SURFACE INDIRECT CONTACT THEREWITH, HEATING SAID SOLUTION THERBY TO A TEMPERATUREABOVE BOTH THE BOILING POINT OF THE SOLUTION AND THE MELTING POINT OFTHE SARCOSINATE, VAPORIZING SUBSTANTIALLY ALL OF THE AQUEOUS SOLVENTFROM SAID SOLUTION AND MELTING THE SUBSTANTIALLY DRY SARCOSINATE THUSFORMED BEFORE CONTACT WITH ANY SUBSTANTIAL AMOUNT OF GAS OTHER THAN SAIDVAPOR, FORMING THE MOLTEN DRIED SARCOSINATE INTO DISCRETE LIQUIDDROPLETS, AND COOLING SAID DROPLETS TO RIGID SOLID PELLETS FO DRYSARCOSINATE.